#include <fstream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <bitset>
#include <queue>
#include <cmath>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int N, M, X[500002], Y[500002], sol[500002], a[500002], nr, x, y;
bitset < 500002 > viz;
vector < int > G[200002];

bool ok()
{
    for (int i=1; i<=N; ++i)
        if (G[i].size()%2) return 0;
    return 1;
}

inline void euler(int nod)
{
    vector < int >::iterator it=G[nod].begin();
    for (; it!=G[nod].end(); ++it)
        if (!viz[*it])
        {
            viz[*it]=1;
            euler(X[*it]+Y[*it]-nod);
        }
    sol[++nr]=nod;
}

int main()
{
    f>>N>>M;
    for (int i=1; i<=M; ++i)
    {
        f>>x>>y; X[i]=x; Y[i]=y;
        G[x].push_back(i);
        G[y].push_back(i);
    }

    if (!ok()) g<<-1<<'\n';
        else
        {
            euler(1);
            for (int i=1; i<=M; ++i)
                g<<sol[i]<<' ';
        }
    return 0;
}